Recently, an electronic endoscope having the function as a spectrometer has been proposed as described, for example, in Japanese Patent Provisional Publication No. 2007-135989A. By using such an endoscope, it is possible to obtain a spectral property (a light absorptivity distribution with respect to frequencies) of a living tissue, such as a mucous membrane of a digestive organ, e.g., a stomach or a rectum. It is known that a spectral property of a substance reflects information concerning the types or densities of components contained in the vicinity of a surface layer of a living tissue being an observation target, which is established in a field belonging to academic frameworks of the analytical chemistry. It is also known in this field that the spectral property of a substance consisting of a composite reflects information obtained by superimposing spectral properties of essential components constituting the composite.
There is a case where a substance having a chemical configuration, which is rarely contained in a living tissue of a healthy portion, is contained in a living tissue of a diseased portion. Therefore, the spectral property of a living tissue containing a diseased portion is different from the spectral property of a living tissue containing only a healthy portion. Since the spectral properties of healthy and diseased portions are different from each other as described above, it becomes possible to judge whether or not a living tissue contains a diseased portion by comparing the spectral properties of the healthy portion and the diseased portion.